Replacing the thermostat, took the old one off without marking the wires. Hooked it up by color and we get the furnace when we put it on cool. wires are green, red, yellow & blue (ground wire)on the wall. The new thermostat wires are red, yellow & green. Can you tell me which wires go where correctly?

color code guide
http://www.wifithermostatreviews.com/the-thermostat-wiring-color-code-guide/
from the looks of that wiring someone was not following the color code, So following the code may not help unless there are marks on the board.

I will assume you did not write down what color wire you took of each letter on old thermostat? Sometimes color of wire doesn't matter as some installers will use whatever color. If you noted where each wire was on old thermostat, just put same color wire to same letter on new one. Under normal situation. y is for compressor (cool) G, is for fan (on AC) , RC is 24 volts from transformer for AC side, RH is 24 volt transformer from heat/furnace, and W is for other wire from furnace, is furnace is only 2 wire system. Was there any wire connected to A on old thermostat?

I'm a little confused as to what you got there. What's the model number of the indoor unit? Yes, if black was in W that is where it needs to stay. In a perfect world all colors match letters but maybe you don't have a white colored conductor. BUT, possibly it was damaged or it's just what the installer used. Be sure to turn power off when messing with wires, it is low voltage but the pain of blowing a fuse is not worth it. Keep us posted!

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i would open the furnace and find where the wires are connected inside the panel and you should be able to identify which color wire is hooked up to each terminal.

Is your wiring where it's hooked into the furnace still identifable as to color. If so one way to tell whats what is to remove wires from furnace one at a time and disconnect all wires from base of thermostat. Use a ohm meter and one very long test wire. Hook to known wire on one end and use test wire to check wires on t-stat end. When you read closed circuit reattach wire to furnace and lable t-stat end as to color. Connections on base of thermostat should be marked with R,W,G,and y. Check each wire one at a time and when you know what color each wire is hook t-stat base back up,put cover back on and check out. A much eaiser way if you can identify wire color and existing wire is accessible in basement or whever your furnace is . Discconect wires from furnace and see if you can pull wire back up to thermostat. If you're lucky they won't be stapeled inside wall. If you can move wire easily buy approximate length of new wire at hardware store. Most of them will sell wire by the foot. Strip about 3/4 inch of insulation from each wire and twist all wires from old to new and wrap all of it with electrical tape. Carefully pull new wire to t-stat and connect there and to furnace. Good luck. I hope this helps. Thanks

Go to furnace and shut off power, remove blower door compartment. Inside you will find a control board where thermostat wires are connected. Should look something like this:

R-Red Wire= Power
G-Green Wire= Fan
W-White Wire=Heat
Y=Yellow or Blue Wire=Cooling.

It sounds like you have a bad motor speed. So try this:

With Power Still Off, on the same control board there is a terminal usually marked Cool and Heat. There should also be a couple of terminals that are named park. The wires hooked to these are the fan wires..

Exchange the Heat and Cool wires on the terminal board. Put everything back together and try cooling again, if the fan comes on
then you have a burnt out motor speed. Go back to furnace and change
the heat and cool wires around, next if Cooling had the black wire hooked to it, put yellow or blue on Cooling and black to park.


Note: The reason why you put the blower door back on is because it
has a door switch that if not properly seated, you wont be able to power
up anything

You will need to go to the heating system and see what color wires are hooked to that. Typically the black and white wires will be used unless they used another color due to a bad wire. Hook the colored wires to the R or RH terminal on the thermostat and the other wire to the W terminal. You can also try taking the wires you have and one by one twisting them together and have a second person inform you when the heating system turns on. Take those two wires and hook them to the terminals I mentioned above.

the two wires are hooked to the baseplate at the R terminal and the W terminal. there may be a switch somewhere on thermostat for electric or gas heat. make sure its in gas mode. make sure batteries are fresh and put in correctly in regards to polarity. make sure furnace is on when doing any settings with the thermostat. make sure themostat is set to "heat". make sure themostat is calling for heat (turn way up to be sure its doing that) . check the troubleshooting guide that came with the new thermostat.

Usually when you have the Y terminal on the thermostat (that would be cooling terminal), there should be 4 screws to connect to. They would be R- to transformer, W- to furnace or heat, Y- to outdoor air conditioner and G- to furnace blower.
You might go to the furnace to see where these wires go, they should have the same terminals on the furnace except for cooling, it usually connects to the outdoor unit wire directly.

. your blue is probably common and if you hooked it to Y you shorted the transformer or blew the low voltage fuse. Green is fan, yellow is AC, Red is 24volt. Is it a heatpump or just ac? I think its probably a heat pump and your brown is your Reversing valve it needs to be hooked to O on the new stat. If its a heatpump your tstat must be a 2heat 1 cool stat w/ aux heat. Without knowing what terminals the wire were hooked to on the old stat you may have to look at whats hooked up at airhandler( furnace) and on A/C (heatpump) tobe able to determine what goes where on the new one.